Wave-guide antenna



Sept. 29, 1959 G. J. BROWN WAVE-GUIDE ANTENNA Filed March 28, 1957 IN VEN TOR.

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United States Patent WAVE-GUIDE ANTENNA Gerald J. Brown, Walpole, Mass.,assignor to The Gabriel Company, Cleveland, Ohio, a corporation of OhioApplication March 23, 1957, Serial No. 649,086

6 Claims. or. 343-781) The present invention relates to wave-guideantennas and, more particularly, to antennas of the type embodying asurface reflector cooperating with a slotted waveguide structure.

Various techniques have been proposed and utilized for feedingradiofrequency energy to surface reflecting elements, such asparaboloidal reflectors. A wave-guide transmission line, for example,has been mounted through the vertex region of a paraboloidal reflectoralong the axis of the reflector, with the mouth of the guide terminatingnear the reflector focus. A secondary reflector surface positionedbeyond the mouth of the guide redirects the waves propagated along theguide back upon the paraboloidal reflector, whence the waves aredirected as a beam into space. This same structure has, of course, beenused, also, as a device for receiving radio waves from space. In orderto efiect this radio-wave feeding-anddirecting process efficiently, ithas been proposed toterminate the wave-guide mouth, which may be ofrectangular crossrsection, in a resonant chamber of transversedimensions larger than the smaller Wave-guide transverse dimension.Slots are provided in the surface of the resonant chamber facing theparaboloidal reflector parallel to each of the wider sides of the guide,thereby permitting energy to flow from the slots to the portions of thereflector disposed on each side of the guide, or to permit energy topass from each portion of the reflector into the corresponding slot ofthe resonant chamber.

Among the disadvantages of such systems, is the mechanical complexityofthe structure and the difficulty in fabricating the same. It is usuallycustomary to taper the wave guide as it joins the resonant chamber inorder that the slots in the chamber may be placed close enough togetherwith respect to the wave-length of the radio energy to appearsubstantially as a point source. It is quite difficult and costly,however, to provide these tapers in wave-guide structures, and it isexpensive and complicated to manufacture and assemble the associatedresonant chambers. A further disadvantage of such systems resides in therelatively narrow band of radio frequencies that can be used withtapered guides and resonant chambers.

In United States Letters Patent No. 2,778,016, issued January 15, 1957to Lan I. Chu, there is disclosed a new and improved antenna embodying awave-guide transmission line of this character that is not subject tothe above-mentioned disadvantages and that, on the contrary, is easy andless costly to manufacture, and is adapted for wide-band frequencyoperation. To achieve these ends, the antenna comprises a longitudinallyextending wave guide within the interior of which radio waves ofpredetermined electric-vector polarization may be longitudinallypropagated and provided near its mouth with a pair of slotscommunicating with the interior of the guide through oppositely disposedtransverse side-wall portions of the guide substantially perpendicularto the plane of the said electric vector. A substantially planarconducting surface closes off the mouth of the guide and extends2,907,034 Patented Sept. 29, 11959 2 outward beyond the said side-wallportions of the in a plane substantially parallel to the plane of thesaid electric vector and perpendicular to the longitudinal axis of thewave guide: 'lhis antenna has been found to operate very successfully inpractice. e I

There are occasions, however, where strict limitations are placed uponthe allowable magnitude of radiation sine lobes. In addition, increasedefliciency is sometimes demanded, namely, greater gain for the sameradiation beam width. In my copending applicatiomserial No. 617,048filed October 19, 1956 for Wave Guide Antenna, this end is achievedthrough providing appropriate conductive chambers overlapping thebefore-mentioned radiating slots. Where such antennas are to be employedfor operation over relatively wide frequency bands, however, theconductive chambers may introduce difliculties in providing selectivefrequency operation'because of their fixed dimensions andin providingunsatisfactory impedancematching over the complete frequency bands. Anobject of the present invention, accordingly, is to provide a new andimproved slotted wave-guide structure of the abovedescribed type that,while providing greatly reduced sidelobe radiation and increasedefliciency, also'provides improved wide-band frequency operation andimpedancematching. In summary, this result is accomplished throughconverging the walls'of the slot-overlapping con ductive chamberstowards the closed end of the guide.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in the appended claims.

q The invention will now be described in connection with theaccompanying drawing, Fig. 1 of which is a fragmentary perspective viewof the invention in preferred form, partly broken away to illustrativedetails of construction;

and I a e v Figs. 2 and 3 'are sections upon a somewhat reduced scaletaken upon the lines 2-2 and 3-3 of Fig. 1, respectively, looking in thedirection of the arrows.

A longitudinally extending wave-guide transmission line section 1 ofrectangular configuration is shown pass ing through a rectangular'hole 2in the vertex region of a'paraboloidal'reflector 3 and extending alongthe axis of the reflector. The guide 1 is mounted in the vertex region 2"by bolting a bracket 4 secured thereto to the outer surface ofthereflector 3, shown to the left in Fig. 1. An annular conducting plate 5is mounted upon the inner surface of the reflector in the vicinity ofthe vertex region 2. The guide 1 may be fed with radio energy from, ormay feed radio energyto, a further guide section 9, coupled to the guide1 at the left of the reflector 3, by a conventional wave-guide flangecoupling 7. The further guide section'9 may be connected to a receiveror transmitter, not shown.

The mouth ,or right-hand end 6 of the guide 1 is received in arectangular recess 17, more particularly shown in Fig. 2, formedintermediately of a planar conducting surface or plate 15 disposedpreferably at right angles to the guide 1. The base'or end 18 of therecess 17 thus closes off the mouth 60f the guide 1. Transverse planarrecesses 21, Fig. 2,preferably of rectangular shape, are formed, as bymilling, in oppositely disposed side walls of the wave guide 1,illustrated as the upper and lower walls 16 and 22, near the mouth orend 6 of the guide. Transverse slots 11 are cut, as explained in thesaid Letters Patent and copending application, through theupper andlower walls intermediate the milled recesses 21 to cooperate withthe'inner space of the guide 1, which 7 may be air or any other desireddielectric medium. In

guidev cesses 21, thereby hermetically sealing the slots 11. Thethickness of the Windows 19 preferably corresponds to the depth of therecesses 21 in order that the outer faces of the windows '19 '-may besubstantiallyflush with the adjacent outer surfaces ofthewave-guide 1.The windows 19 may -'be of any desired radio-wave transparent material,such as polystyrene and the like, though a preferred Window isconstituted of Corning Type 707 glass.

As explained in the said Letters Patent and copending application, thedepth of the conducting-surface recess 17 preferably corresponds to,justslightly less than, the dis tance from the mouth 6 of the guidel to theedge of each slot 11 further from the reflector 3, in order that thesaid edge may lie substantially in the plane of-the surface of theconductingplate 15', facingthereflectorS. As will later beexplained,-however, c'ertainvariations in the position of the slot maybe tolerated. The ends of the milledsections 21 0f the guide 1-at themouth 6 maybe secured in place inthe recess 17 by soft solderjthe recess17 being of somewhat larger dimensions than "the transverse guidedimensions in order-to-permit the securing process to be effected withease and to facilitate removal of the same, if necessary. r

Ignoring, for themoment the conducting-chamber surfaces 30 and 32, radiowaves propagated longitudinally along the guide 1 toward its'mouth' 6,in, for example, the TE mode, having vertical electric-vectorpolarization, represented by E, are radiated through the upper and lowerslots 11, the slots lying in planes perpendicular to the electricvector. In the absence of the chambers 30 and 32, the energy radiatedthrough the slots 11' would become initially guided between the upperand lower outer surfaces 16 and 22 of the guide 1 and the adjacentrespective upper and lower portions'14 and 20, Figs. 2 and 3, of. theplate 15 From another point. of view, the slots 111 may be considered asexciting elements disposed substantially along the vertex ofa pair ofsubstantially rightangularly disposed corner guiding surfaces 14-16 and20-22. The energy would thus be directed'back along theupper and lowerouter surfaces ofthe guide 1, refleeting from the upper and lowersurface portions and 12 of the reflector 3, thereby being directed as abeam into space, as explained in the said Letters Patent and copendingapplication. Since the separation between the upper andlower guideside-walls '16 and 22 of a rectangular guide operated as above describedcan be made small compared to the wavelength of the radio energy, theslots 11 are rather close together and for all practical purposes behavesubstantially as a single point source, thus taking advantage of theparallel-ray focusing properties of the paraboloidal reflector 3 toproduce the beforementioned directive beam in space. The reverse processtakes place in reception of energy from space.

The optimum position of the slots 11 for producing the most satisfactoryundistorted major radiation lobe in the plane of the electric vector,consistenfwith maximum antenna gain, has been found to be thatpreviously described with the slot 11 lying just outside the plane ofthe inner surface of the conducting plate 15. It has been determined,however, that satisfactory, though less desirable, results can beobtained if the slots 11 are disposed somewhat closer to theparaboloidal reflector 3, though intolerable distortion of the radiationlobe pattern and loss of antenna gain has been found to occur if theslots 11 are spaced closer to the reflector 3 than about onequarter ofthe wavelength of the radio energy from the position shown in Figsv 1and 2. It has also been determined that the transverse dirnension of theupper and lower portions 14 and 2 0 of the plate 15 should have a .valuenot greater than one-half of the said wavelength for the wide-bandoperation and impedance-matching purposes of the: present invention. Thelength of the slots '11 'is rather critical, though variations-in thewidth of the slots may be'effected. 'Undesirable' efiects produced bythat energy which is reflected'from "the Ifltor 3 back into the slots 11may be minimized with the aid of the previously described plate 5superimposed upon the reflector 3 about the guide 1. While some energyreflected from the outer portions of the reflector 3 may re-enter theslots 11, cancellation or substantial cancellation thereof at the slots11 has been found to occur as a result of reflections from the surfaceof plate 5 protruding closer to the slots 11 than the adjacent portionsof the reflector 3. This effect, moreover, takes place over a relativelybroad band of frequencies.

' In accordance with the present invention, however, the slots 11 arenot left free to radiate upward and downward into space as in theantenna of the said Letters Patent. To the contrary, upper and lowerhollow conductive-chamber surfaces 30 and 32 are provided extending fromthe upper and lower end-plate surfaces 14 and 20 back toward thereflector 3. As is explained in the said copending application, it hasbeen found that if, first, the length W, Fig. 2, of these chambers 30and32 is sufficient to overlap the slots 11 and to extend atleastsubstantially a half-Wavelength from the end plate 15, and even up tosubstantially three-quarters of the wavelength; and, if,

secondly, the maximum chamber height is about a halfwavelength, but notgreater than substantially threequarters of a Wavelength, an extremelybeneficial result takes place. That result is thevastly improvedreduction in side lobes of the radiation pattern and increased radiatingefliciency. The explanation of this experimentally verified result mayreside in the fact that the chambers 30 and 32 will be excited byradiation through the slots 11, acting as wave-guide radiators havingsubstantially the same modeof electromagnetic field as the originalguide 1. The radiation that normally spills over or is wasted when theslot radiation upward and downward is unconfined, as-in the antenna ofthe said Letters Patent, contributes to the production of side lobes andthe diminution of energy in the primary radiation lobe or pattern. Sincethis slot-radiated energy is now confined to travel through the chambers'30 and 32 directly rearward toward the reflector 3, more energy ismaintained in the primary lobe, resulting in greater efliciency andmarkedly reduced side-lobe radiation.

While, in some cases, as further explained in the said copendingapplication, the chambers 30 and 32 might constitute merely walls of acylinder extending rearward from the complete peripheral border of theplate 15, it is often desirable to maintain the horizontal radiationpattern relatively broad. This may be achieved by limiting the maximumtransverse-dimension-of the chambers 30 and 32 to the width of the guide1,- as by terminating the surfaces 30 and 32 at the side walls of theguide 1, as shown more particularly; in Fig. 3. Other surfaceconfigurations 30 and 32, including rectangular chambers, may also beemployed, though the illustrated oval configuration has been found tooperate very satisfactorily.

Not only does the above-described construction eliminate thenecessity-for tapering the wave guide and for providing resonant slottedchambers, but this construction is admirably suited to rapid andaccurate mass-production techniques. It has been observed that thisstructure, in addition, illuminates or feeds the reflector aperturein'such, a manner as to provide greatly reduced secondary lobes in theradiation pattern and increased efficiency.

In accordance with the present invention, however, the chambers 30 and32 are so designedas to prevent frcquency-selective operation that isnormally inherent in fixed-chamber systems and poor impedance matchingat particular frequencies in a relatively wide band of frequencies withwhich theantenna is to be employed. It has been found that by causingthe chambers to converge substantially conically toward the end plate 15closing off the waveguide mouth 6, this very desirable end of wide-bandfrequency operation can be achieved. With regard to wide-band impedancematching, it should be observed that two problems are presented: first,wideband matching between the slots 11 and the chambers 30 and 32; andsecondly, wide-band matching between the chambers 30 and 32 and thespace between the chamber mouths 30' and 32' and the reflector 3.Fortunately, the converging construction before mentioned has beendiscovered simultaneously to accomplish both of these widebandimpedance-matching efiects, particularly when the uppermost andlowermost portions of the chambers 30 and 32 are provided withsubstantially planar intermediate regions-130 and 132, corresponding tothe intersection with the substantially conical chambers 30 and 32 ofplanes extending from substantially the uppermost and lowermost portionsof the apertures 30 and 32 toward the end plate 15.

The optimum angle a of convergence of the substantially conical chambers30 and 32 with their preferably substantially planar upper and lowerregions 130 and 132, Fig. 2, has been found to be substantiallythirty-two and a half degrees, with highly satisfactory results forvarious purposes obtainable with angles a differing by as much assubstantially :25 percent from that optimum angle.

In order to simulate a point source, as before mentioned, the slots :11may be brought closer together by reducing the height of the terminalsection of the guide 1 containing the slots 11. The point of transition1' between the left-hand greater-dimensional guide section 1 and thesaid terminal section should be located sufliciently rearward of theapertures or mouths of the chambers 30 and 32 to prevent restriction ofthe energy directed therefrom. A guide 1 of uniform dimensionsthroughout, however, may be employed, if desired. The apertures ormouths of the chambers 30 and 32 may be covered with I weatherproof,radio-wave permeable windows 30, 32', as of A of an inch thickpolystyrene and the like.

As an illustration of typical dimensions, given in units of inchesinstead of fractions of a wavelength, though they may easily beconverted into such, an antenna for operation over the band of from 6875to 7125 megacycles may utilize a TE -mode-operated wave guide 1' havingside walls about of an inch thick. The recesses 21 may be about of aninch deep and about A of an inch wide. The slots 11 may be about 7 of aninch long and of an inch wide and spaced about of an inch from the mouth6 of the guide 1. The depth of the recess 17 in the conducting plate '15may also be about of an inch for optimum results. The chambers 30 and 32may be of overall length W about one inch; the plate 15 may have aheight of of an inch; the chamber apertures or mouths 30' and 32 mayhave a height of about /1 of an inch; the substantially conical chambers30 and 32 may have a transverse radius of about three-quarters of aninch, and an angle of convergence or of about 32 /2 degrees.

Extremely low-energy secondary lobes have been produced with thisstructure in the vertical and horizontal radiation pattern,respectively, with substantially constant voltage standing-wave ratios,indicating impedance matching of substantially 1.06 at the low end ofthe band, 1.10 at the mid-band frequency, and 1.05 at the high end ofthe band.

While, as before explained, the rectangular guide 1 is particularlywell-suited to the purposes of the present invention inasmuch as theheight dimension, shown vertical, may be small compared to the wavelength of the radio energy, so that the slots 11 may be close together,if some distortion can be tolerated, the same technique may be appliedto wave guides of other configuration, such as guides that are oval,including substantially circular, in cross section.

While, moreover, the invention has heretofore been described inconnection with the use of such systems as transmitting apparatus, it isto be understood that they are equally well suited for the reception ofradio waves. The slotted wave guide and end-plate structure, moreover,

utilized where symmetrical results are not wanted. A

plurality of unsymmetrically disposed slots may also be employed, ifunsymmetrical patterns are to be achieved, the plurality of slots, forexample, being parallel to one another on one side only of the guide.While the slots 11 have been shown as provided with rounded ends, thisis merely because a milling machine may produce such ends. It is to beunderstood, however, that the slots may be of strictly rectangular orother configuration and that they may be formed by punching and otherprocesses as well. Similarly the plates 15 may be of other configurationthan rectangular. The length and orientation of the slots may also bevaried depending upon the desired radiation pattern configuration. As afurther illustration, the terminal slots may be provided in the narrowerside walls parallel to the wave-guide axis and perpendicular to the endplate 15.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within thespirit and scope of the inventionas defined in the appended claims.

What is claimed is:

l. A longitudinally extending wave guide of substantially rectangularcross section closed at one end having a slot in a wall of the guidenear the said end, and a conducting surface spaced from and extendinglongitudinally back along the said wall overlapping the said slot andconverging toward the said end of the guide,-the said conducting surfaceterminating along its side edges at the side edges of the said wall ofthe guide.

2. A longitudinally extending wave guide closed at one end having a slotin a predetermined portion of wall surface of the guide near the saidend, and a conducting surface spaced from and extending longitudinallyback along the said predetermined portion of wall surface and shaped toprovide a chamber between the said predetermined portion of wall surfaceand the conducting sur-- face converging toward the said end of theguide and overlapping the said slot in order to be excited by radiationpassing through the slot, the chamber terminating at the sides of thesaid predetermined portion of wall surface in order to provide a chamberaperture the width of which corresponds to the width of the guidebetween the sides of the said wall.

3. A longitudinally extending wave guide closed at one end having a slotin a predetermined portion of wall surface of the guide near the saidend, a first conducting surface disposed at an angle to the wave guideat the said end and extending transversely beyond the said predeterminedportion of wall surface, and a second conducting surface extendinglongitudinally from the first conductmg surface'back along the saidpredetermined portion of wall surface and shaped to provide a chamberhaving the said predetermined portion of Wall surface and the firstconducting surface as its other bounding surfaces and overlapping thesaid slot in order to be excited by radiation passing through the slot,the chamber terminating at the sides of the said predetermined portionof wall surface in order to provide a chamber aperture the width ofwhich corresponds to the width of the guide between the sides of thesaid predetermined portion of wall surface, and the second conductingsurface converging with the said predetermined portion of wall surfaceof the guide toward the said end thereof.

4. A longitudinally extending wave guide closed at one end having a slotin a predetermined portion of wall surface of the guide near the saidend, a first conducting surface disposed at an angle to the wave guideat the said end and extending transversely beyond the said predeterminedportion of wall surface, and a second conducting surface extendinglongitudinally from the first conducting surface back along the saidpredetermined portion of wall surface and shaped to provide a chamberhaving the said predetermined portion ofi wall surface and the firstconducting surface as its other bounding surfaces and overlapping thesaid slot in order to be excited by radiation passing through the slot,the chamber being of oval cross-section substantially conical in surfaceconverging toward the said end of the guide and terminating at the sidesof the said predetermined portion of wall surface in order to provide achamber aperture the maximum width of which corresponds to the width ofthe guide between the sides of the said predetermined portion of wallsurface. a

5. A longitudinally extending wave guide closed at one end having a pairof slots in oppositely disposed side wall surface portions of the guidenear the said end, a first conducting surface disposed at substantiallyright angles to the said side wall surface portions of the Wave guide atthe said end and extending transversely beyond the said side wallsurface portions, and further conducting surfaces extendinglongitudinally from the first conducting surface back along the saidside wall surface portions and shaped to provide substantially conicalchambers overlapping the said slots in order to be excited by radiationpassing through the slots and converging toward the said end of. theguide, the chambers terminating at the sides of the said side wallsurface portions of the guide in order to provide chamber apertures thewidth of which correspond to the width of the guide between the saidsides of the said wall surface portions.

6. A wave guide as claimed in claim 5 and in which the cross-sectionalconfiguration of the guide is substantially rectangular and the saidside wall surface portions are substantially parallel to one another.

References Cited in the file of this patent UNITED STATES PATENTS2,566,900 McArthur Sept. 4, 1951 FOREIGN PATENTS 708,614 Great BritainMay 5, 1954

